This paper reports the results of
an experimental workconductedtoinvestigatetheeffectofcuringconditionsonthecompressivestrengthofself-compactinggeopolymerconcreteprepared by using fly
ash as base material and combination of sodiumhydroxide and sodium silicate as alkaline activator. The
experimentswere conducted by varying
the curing time and curing temperature intherangeof24-96hoursand60-90°Crespectively.TheessentialworkabilitypropertiesoffreshlypreparedSelf-compactingGeopolymerconcretesuchasfillingability,passingabilityandsegregationresistancewereevaluatedbyusingSlumpflow, V-funnel,L-boxandJ-ringtestmethods.ThefundamentalrequirementsofhighflowabilityandresistancetosegregationasspecifiedbyguidelinesonSelf-compactingConcretebyEFNARCwere satisfied. Test
results indicate that longer curing time and curingtheconcretespecimensathighertemperaturesresultinhighercompressivestrength.Therewasincreaseincompressivestrengthwiththeincreaseincuringtime;howeverincreaseincompressivestrength after 48 hours was not significant.
Concrete specimens curedat70°Cproducedthehighestcompressivestrengthascomparedtospecimens cured at 60°C, 80°C and 90°C.

In thegrowingenvironmentalconcernsofthecementindustry,alternativecementtechnologieshavebecomeanareaofincreasinginterest.Itisnowbelievedthatnewbindersareindispensableforenhancedenvironmentalanddurability performance. In this aspect, geopolymer technologyisoneoftherevolutionarydevelopmentsrelatedtonovelmaterialsasanalternativetoPortlandcement.Thedevelopmentofgeopolymerconcreteisanimportantstepbecause of the potential application of
geopolymers to a widevarietyofindustrialwastematerialstoproduceadded-valueconstructionmaterialsresultinginlow-costandenvironmentally friendly material with similar mechanicalperformance and appearance properties to
those from Portlandcement .Geopolymerconcreteisproducedbyactivatingdifferentalumino-silicatebasedwastematerialswithhighlyalkalinesolution.Curingoffreshlypreparedgeopolymerconcrete is the most
crucial aspect and plays an important roleinthegeopolymerisationprocess.Propercuringofconcretehasapositiveeffectonthefinalpropertiesofthegeopolymerconcrete.Curingof geopolymerconcreteismostlycarriedoutatelevatedtemperatures ,however,
curingatambienttemperatureshasalsobeencarriedout.Atambienttemperatures;thereactionofflyash-basedgeopolymericmaterialsisveryslowandusuallyshowaslowersettingandstrengthdevelopment.Itisbelievedthathigher temperatures
activate alumino-silicate phases in the flyash,therefore,theyaregenerallycuredatelevatedtemperatures between 60 0 C- 90 0 C.

Previousresearchhasshownthatbothcuringtimeandcuringtemperaturesignificantlyinfluencethecompressivestrength of geopolymer
concrete. Several researchershave
investigated the effect of curing time and curingtemperature on the properties of geopolymer
concrete,intheirstudyonflyash-basedgeopolymershavereportedthatthecuringtemperatureandcuringtimesignificantly affected the mechanical
strength of fly ash-basedgeopolymers.Theyconcludedthathighercuringtemperatureand longer curing
time proved to result in higher compressivestrength.

westudiedtheinterrelationshipofcertain parameters that affected the properties of fly ash-based geopolymer.Theyhavedemonstratedthatwatercontent, curing time and
curingtemperature affected the
properties ofgeopolymers;specificallythecuringconditionandcalciningtemperatureinfluencedthecompressivestrength.Theyconcludedthatrapidcuringandcuringathightemperaturereduced the compressive strength and caused a
negative effecton the physical
properties of the geopolymer.

Inastudy donewe oncompressive strength and
microstructural characteristics of class Cfly ash geopolymer, the authors
have reported that curing temperature hadasignificanteffectonthecompressivestrength development.Compressivestrengthbegantodecreaseafter curing
for a certain period of time at higher temperature. They revealedthatprolongedcuringcanbreakdownthegranular structure of the geopolymer mixture.

Iinhisresearchstudyoneffectofcuringtemperatureonthedevelopmentofhardstructureofmetakaolin-basedgeopolymer,hasreportedthatcuring temperature had significant effect on the setting and
hardeningofmetakaolin-basedgeopolymer.Theauthorhasdemonstratedthathighercuringtemperaturesandlongercuringtimeincreasetheearlyagecompressiveandflexuralstrengths. However, elevated temperature during early stage ofhardeningprocessresultstotheformationoflargerporesconsequentlyincreasescumulativeporevolume,whichhasanegativeeffectonthefinalmechanicalpropertiesofgeopolymeric material.

Thisstudyaimedtoanalyzetheeffectofcuringtimeandcuringtemperatureonthecompressivestrengthofflyash-basedself-compactinggeopolymerconcrete.Testresultsindicatethatlongercuringtimeandcuringtheconcretespecimens at elevated temperature up to 70 0
C result in highercompressive strength.

II.EXPERIMENTAL DETAILS

A.Materials

In the present study, Low-calcium
(ASTM Class F) Fly ashwas used as a
source material for the synthesis of SCGC. Flyash was obtained from Manjung power station, Lumut, Perak, Malaysia.The
chemical composition of Fly ash as determinedby X-Ray Fluorescence (XRF) analysis is shown in Table I.

Toachievehigherworkabilityandrequiredflowabilityofthefreshconcrete,acommerciallyavailablesuperplasticizer(SikaViscocrete-3430)suppliedbySikaKimiaSdnBhd,Malaysia,andaspecifiedamountofextrawater(otherthanthewaterusedforthepreparationofsodiumhydroxidesolution) was also used.

TABLE
I

CHEMICAL
COMPOSITION OF FLY ASH AS DETERMINED BY XRF

Oxide (%) by mass

Silicon dioxide (SiO 2 ) 51.3

Aluminum oxide (Al 2 O 3 )30.1

Ferric oxide (Fe 2 O 3 )4.57

Total SiO 2+ Al 2 O 3+ Fe 2 O 385.97

Calcium oxide (CaO)8.73

Phosphorus pentoxide (P 2 O 5 )1.6

Sulphur trioxide (SO 3 )1.4

Potassium oxide (K 2 O)1.56

Titanium dioxide (TiO 2 )0.698

B.Design
of Mix Proportion

Inthisexperimentalwork,amixproportionwiththecontentof400kg/m 3offlyashwasdesignedtostudytheeffectofcuringtimeandcuringtemperatureonthe compressive strength of
self-compacting geopolymer concrete. Four levels of curing time i.e. 24, 48, 72
and 96 hours and fourranges of curing
temperature i.e. 60°C, 70°C, 80°C and 90°Cwereused.ThedetailsofthemixproportionaregiveninTable II. In order to attain required
workability characteristicsofself-compactinggeopolymerconcrete,awatercontentof12% and superplasticizer dosage of 7% by mass
of the fly ashwere also used. The
alkaline solution-to-Fly ash ratio was kept0.5 whereas the ratio ofsodiumsilicatetosodiumhydroxideandconcentrationofsodiumhydroxidewere2.5and12Mrespectively.

TABLE
II

DETAILS
OF MIX PROPORTION

Fly Ash (Kg/m 3 )400

Fine Aggregate (Kg/m 3 )850

Coarse Aggregate (Kg/m 3 )950

Sodium Hydroxide (Kg/m 3 )57

Concentration of NaOH Solution (Molarity)12

Sodium Silicate (Kg/m 3 )143

Super plasticizer (%)7

Extra water (%)12

Sodium Silicate/Sodium hydroxide by mass2.5

Alkaline to Fly ash ratio0.5

Curing time (hrs)24-96

Curing temperature (°C)60-90

C.Mixing
Procedure

Mixing was carried out in two
stages. Initially, Fly ash, Fineaggregate (in dry condition) and coarse aggregate (in saturatedsurface dry condition) were mixed in a pan
mixture for about

2.5minutes. At the end ofthismixing, theliquid componentofthegeopolymerconcretemixturecomprisingalkalinesolution, superplasticiser and the extra water, was added to the solid particles and the mixing continued for
another 3 minutes.Toensurethemixturehomogeneity,freshconcretemixwashandmixedforfurther2to3minutes.Thefreshlypreparedconcretemixwasthenassessedfortheessentialworkabilitytestsrequiredforcharacterizingself-compactingconcrete(SCC). Tests such as slump flow,
slump flow at T 50 , V-funnel, L-box, and J-ring were performed for this
purpose.

D.Casting
and Curing of Test Specimens

AfterassessingthenecessaryworkabilitypropertiesasguidedbyEFNARC[11],thefreshconcretewasplacedinsteel moulds of dimensions 100 x 100 x 100 mm and allowedtofillallthespacesofthemouldsbyitsownweight.Threecubeswerepreparedforeachtestvariable.Aftercastingthemoulds,withoutanydelay,theywerekeptintheovenataspecifiedtemperatureforaspecifiedperiodoftimeinaccordance with the test
variables selected. At the end of thecuringperiod,themouldsweretakenoutfromtheovenandleft undisturbed for about 15 minutes. The
test specimens wereremovedfromthemouldsandlefttoairdryintheroomtemperatureconditionsuntiltestedfordirectcompressionatthe
specified age.

III. RESULTS AND DISCUSSION

A.Fresh Properties of SCGC

The
properties of fresh SCC differ significantly from that ofconventionalfreshconcrete.TherearethreedistinctfreshpropertiesofSCCwhicharefundamentaltoitsperformanceboth in fresh and
hardened state. According to EFNARC [11],aconcretemixcanonlybeclassifiedasSCCiftherequirementsforallthethreeworkabilitypropertiesarefulfilled. The three
essential fresh properties required by SCCare filling ability, passing ability and resistance to segregation. To
accomplish the workability properties, tests such as slumpflow,slumpflowatT50,V-funnel,L-box,andJ-ringwerecarriedout.AllthetestswereperformedbyfollowingtheEuropeanGuidelinesforSCC.Thetestresultsoffreshproperties of SCGC are
presented in Table III. The results ofthe quantitative measurements and visual observations showedthatfreshlypreparedconcretemixhadgoodflow,filling& passing ability, and produced desired
results and were withinthe EFNARC range
of SCC.

TABLE III

WORKABILITY TEST RESTULTS

Workability
Test Results Acceptance Criteria for SCC

As per EFNARC [11]

MinimumMaximum

Slump
flow (mm)710650 mm800
mm

T
50 cmSlump flow (sec.)4.02 sec.5 sec.

V-Funnel
Flow time (sec.)76 sec.12 sec.

L-Box
(H 2 /H 1 )0.960.81.0

J-Ring
(mm)50 mm10 mm

B.Compressive
Strength of SCGC

Compressive
strength is one of the most common measuresusedtoevaluatethequalityofhardenedconcreteandisconsideredasthecharacteristicmaterialvaluefortheclassificationofconcrete.Manyresearchershaveusedcompressivestrengths measurementsasatooltoassessthesuccessofgeopolymerisationprocess[12].Compressivestrength test was performed in accordance
with BS EN 12390-3:2002using 2000KNDigitalCompressive&FlexuralTesting Machine. At the
end of specified oven curing period, aset of three cubes for each test variable was tested at the agesof 1, 3, 7 and 28 days. The compressive
strength test resultsare presented in
Table IV. The reported compressive strengthis the average strength of three specimens.

TABLE IV

COMPRESSIVE STRENGTH TEST
RESTULTS

Compressive Strength Test Results

Mix1-Day3-Day7-Day28-Day

(MPa)

S145.0145.8546.9448.53

S2 51.0351.9852.2653.80

S351.4152.2052.6953.92

S451.6852.3352.7253.99

S544.8145.6445.9847.54

S651.0351.9852.2653.80

S748.5649.2249.8050.77

S847.9948.8349.6750.42

1.Effect
of Curing Time on Compressive Strength

Fig.1showstheinfluenceofcuringtimeonthecompressive strength of self-compacting
geopolymer concrete.The test specimens were cured in the oven at a temperature
of70°C.Thecuringtimevariedfrom24hoursto96hours (4days).Itisbelievedthatlongercuringtimeimprovedthegeopolymerisationprocess resultinginhighercompressivestrength.ThetestresultsshowninFig.1indicatethatthecompressivestrengthincreaseswithincreaseincuringtime. Thetestspecimenscuredat70°Cforaperiodof96hoursproduced the highest compressive strength at
all ages. The rateof increase in
strength was rapid up to 48 hours of curing time; however,thegaininstrengthbeyond48hoursisnotsignificant.TheresultsshowninFig.1clearlydemonstratethatlongercuringtimedoesnotproduceweakermaterialasclaimed .Thetrendofthesetestresultsissimilartothoseobservedbyin their study on Fly ash-based geopolymer
concrete.

2.Effect
of Curing Temperature on Compressive Strength

Curingtemperatureplaysasignificantroleinthesettingand hardening of the
geopolymer concrete [2]. Hardjito et al. [14], in their study on low-calcium
Fly ash-based geopolymermortarhavereportedthatcuringtemperatureplaysanimportantroleinthegeopolymerizationprocessofFlyash-based geopolymer. They have concluded
that higher the curingtemperature,higherwillbetherateofgeopolymerizationprocess,whicheventuallyacceleratesthehardeningof

geopolymer
mortar.

TheeffectofcuringtemperatureonthecompressivestrengthisillustratedbythetestdatashowninFig.2.Ascuring of fly ash-based geopolymer concrete is usually carriedoutatanelevatedtemperatureintherangeof60-90°C;therefore,inthisexperimentalstudythecuringtemperaturewas varied from 60 to 90°C. The test
specimens were cured inthe oven at a
temperature of 60, 70, 80 and 90°C for a periodof 48 hours. All the other test parameters were kept constant.

Itisbelievedthatincreaseinthecuringtemperaturefrom60°C to 70°C increased the rate and extent of
reaction throughan increase in the heat
of reaction; consequently increased thecompressive strength of the concrete.

Fig. 2 Effect of Curing
Temperature on Compressive Strength

V.
CONCLUSION

In
this experimental work, the effect of curing conditions onthecompressivestrengthofflyash-basedself-compactinggeopolymerconcretewasinvestigated.Testresultsindicatethat curing time and curing temperature significantly affect thecompressive strength of hardened concrete.
Based on the testresults reported here,
the following conclusions can be drawn.